9514 1404 393
Answer:
48 kph
Step-by-step explanation:
The distance is immaterial, as long as it is the same at both speeds. The total time for some distance d is ...
t = d/40 +d/60
And the average speed is ...
2d/t = 2d/(d(1/40 +1/60) = 2/(1/40 +1/60) = 2(40)(60)/(40+60) = 4800/100 = 48
The average rate for the round trip is 48 kph.
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Additional comment
This value is called the harmonic mean of the two speeds. It is the reciprocal of the average of the reciprocals of the speeds.
